Engine systems may be configured with boosting devices, such as turbochargers or superchargers, for providing a boosted aircharge and improving peak power outputs. The use of a compressor allows a smaller displacement engine to provide as much power as a larger displacement engine, but with additional fuel economy benefits. A charge air cooler (CAC) may be provided downstream of the compressor for cooling the boosted aircharge, thereby increasing the charge density, before it is delivered to the engine intake. As such, the charge air cooler may be coupled to a coolant loop that is distinct from, and not connected to, the engine coolant loop used to heat/cool the engine. Due to this separation, the charge air cooler may run at cooler temperatures (e.g., ambient temperatures) for extended durations. When EGR is introduced upstream of the charge air cooler, condensation can occur. When ingested, the condensate can cause misfires and NVH issues.
One approach to intermittently warm the CAC is taught by Vigild et al. in US 2012/0297765. Therein, the charge air cooler is fluidly connected to each of the engine cooling circuit and the CAC cooling circuit via a plurality of valve devices. By opening a first valve during a first set of conditions, the CAC cooling circuit is exposed to hotter coolant from the engine cooling circuit, enabling a periodic raising of the temperature of the CAC cooling circuit. In comparison, by opening a second valve during a second set of conditions, the CAC cooling circuit is exposed to cooler coolant from the CAC cooling circuit, enabling a lower temperature of the CAC cooling circuit to be maintained.
However the inventors herein have identified potential issues with such an approach. As one example, during cold start conditions, coolant temperatures in the engine cooling circuit may not be high enough to transfer sufficient heat to the CAC cooling circuit. During such conditions, the introduction of any EGR can lead to condensation build up at the CAC. While the CAC can be warmed using engine heat, it requires prior engine warm-up which can be slow during an engine cold-start. In addition, the approach of '765 requires the use of additional components, such as valves and fluid passages, which may increase cost and complexity of the system. Further still, turning off the cooling circuit pump limits heat transfer to the ambient.
Thus in one example, the above issues may be at least partly addressed by a method for a boosted engine comprising: closing a wastegate and an EGR valve while opening a compressor recirculation valve to heat a charge air cooler coupled downstream of a compressor responsive to cold conditions. In this way, transferring of turbine energy to the intake air may be used to warm the intake aircharge and increased compressor recirculation flow of the heated aircharge can be used to warm the charge air cooler.
For example, an engine system may include an intake compressor with a compressor bypass coupling an outlet of a downstream charge air cooler (CAC) to an inlet of the compressor. By adjusting the position of a compressor recirculation valve (CRV) in the compressor bypass, an amount of (cooled) compressed air may be recirculated from downstream of the CAC to the compressor inlet. The CAC may be coupled to a cooling circuit. The engine system may further include an exhaust turbine for driving the compressor, with a wastegate coupled in a bypass across the turbine. During cold conditions, such as when the CAC has been below a threshold temperature for an extended period of time, during an engine cold-start, or when ambient conditions are cold, an engine controller may actively close the wastegate to increase the exhaust pressure and spin the turbine. By recovering exhaust energy via the turbine and transferring energy to the intake air, the temperature of the CAC and the incoming intake air is increased. By simultaneously opening the CRV, the heated aircharge can be recirculated around the compressor and the CAC, thereby expediting warming the CAC. In addition, by increasing the recirculation of heated air across the CAC (via the CRV), heat transfer to the CAC (and the CAC cooling circuit) is increased without incurring a substantial increase in throttle inlet pressure.
An EGR valve may be maintained closed while the wastegate is closed and the CRV is opened so that the delivery of EGR is delayed until the CAC is sufficiently warm. Once the CAC temperature is above a threshold temperature, the EGR valve may be opened. By introducing EGR only after the CAC is sufficiently warm, the propensity for condensation and the associated issues are reduced. Increased delivery of low pressure EGR following warming of the CAC can be used to expedite engine heating. Specifically, as EGR is introduced, heat may be rejected by an EGR cooler to the engine cooling circuit to thereby warm up the engine.
In this way, exhaust heat may be recovered via a wastegate and added to a CAC during cold conditions to expedite warming of the CAC during cold engine conditions. By expediting warming of the CAC, EGR benefits can be achieved during low ambient conditions. By increasing the window for EGR operation without condensation, the overall fuel economy can be improved. By delaying introduction of EGR to a compressor inlet until the CAC has been warmed, EGR condensation is reduced. As such, this reduces the occurrence of misfires and other condensate ingestion related NVH issues.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.